Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, and the description corroborates with "Read-only; nothing is created or changed." It adds genuine behavioral context annotations cannot carry: every project has its own currency independent of the Invio business currency, and a 401/unauthorized failure may mean the Xero plan lacks Projects or the connection needs reconnecting rather than a generic error. It stops short of describing pagination behavior beyond the schema fields.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with purpose and scope before the caveats, and nearly every clause carries operational value. Slightly overlong: the currency warning is stated twice ("Each project carries its OWN currency..." and "every money figure names its own currency alongside its value"), which could be tightened into one sentence.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description compensates by describing what each result carries (headline estimate/invoiced/still-to-invoice figures, per-project currency) and by pre-explaining the most likely failure mode. An agent has everything needed to call this correctly and interpret the response.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description adds real meaning: contactId is tied to a Xero ContactID obtainable from list_xero_contacts, and state is characterized as INPROGRESS/CLOSED with the omit-for-both default. page and pageSize are left entirely to the schema, which documents them adequately.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a concrete verb and resource ("List job/project-costing projects from Xero Projects for the current organisation") and immediately grounds it with what a project represents ("the jobs or engagements time, expenses and invoices get tracked against"). It also explicitly distinguishes itself from the sibling get_xero_project, which returns the full breakdown for one project.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit when-to-use routing: this tool for the list view, get_xero_project for the full cost-and-earned breakdown on a single project. It also states the filtering conditions (one contact, one state, or neither) and where a valid contactId comes from (list_xero_contacts).

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.